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We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn 1−x Fe x O 3+y , in the whole range 0.0Յ x Յ 1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn-Teller distortion, thus favoring a ferromagnetic ͑FM͒ superexchange interaction between Mn 3+ -O-Mn 3+ . For x = 0.0 the oxygen excess ͑y Ϸ 0.09͒ produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn 4+ ions and 82% of the usual Mn 3+ ions, with possible double-exchange interaction between them. The Fe doping in this system is known to produce only stable Fe 3+ ions. We find an evolution from a fairly strong FM phase with a Curie temperature T C ϳ 160 K, for x = 0.0, to an antiferromagnetic ͑AFM͒ phase with T N = 790 K, for x = 1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease ͑increase͒ in the FM ͑AFM͒ phase, accompanied by a systematic transition broadening for 0.2Ͻ x Ͻ 0.7. A model based on the expected exchange interaction among the various magnetic-ion types accounts very well for the saturation magnetization ͑M S ͒ dependence on Fe doping.

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The magnetic and superconducting properties of RuSr 2 Gd 1.5 Ce 0.5 Cu 2 O 10−␦ polycrystalline samples with different oxygen-doping levels are presented. A strong suppression of the superconducting temperature ͑T c ͒, as well as a reduction in the superconducting fraction, occurs as the oxygen content is reduced by annealing the samples in oxygen-deprived atmospheres. Drastic changes in the electrical resistivity are observed above T c , possibly associated with oxygen removal, mainly from grain boundaries. However, the magnetic ordering is relatively less affected by the changes in oxygen content of the samples. The spin-glass transition is enhanced and shifted to higher temperatures with the reduction in oxygen content. This could be correlated with an increase in the spin disorder and frustration for the oxygen-depleted samples. Also, the same oxygen-vacancyinduced disorder could explain the reduction in the fraction of the sample showing antiferromagnetic order. We also report significant changes in the measured properties of the samples as a function of time.

The crystal structure and some magnetic properties were investigated for polycrystalline samples of LaMn1−xFexO3+y, prepared by solid-state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn–Teller distortion and favors a ferromagnetic (FM) superexchange interaction between Mn3+–O–Mn3+. An evolution from a fairly strong FM phase, for x=0.0, to an antiferromagnetic (AFM) phase, for x=1.0, was observed. For intermediate Fe contents, a magnetic mixed-phase state occurs, with a gradual decrease (increase) in the FM (AFM) phase as x increases. A clear cluster-spin-glass (CG) behavior is observed in our samples for x≤0.1, where FM coupling dominates. In this case, the Vogel–Fulcher law describes very well the CG dynamics, giving reasonable values for the fitted parameters.